1. Field of the Invention
This invention relates to an electroluminescent display and circuit protective devices, and methods of making the same. More particularly, this invention relates to such devices having external conformal contacts and methods of making the same. This invention further relates to such devices having plastic encapsulated bases with wrap-around contacts formed about opposed ends of the bases. Also, this invention relates to such devices having a protective element, such as a fuse, electrically coupled between its contacts, so that such devices may be used for circuit protection purposes.
As used herein, electroluminescent refers to radiation from electrically excited solid-state elements.
2. Description of the Prior Art
Electroluminescent display devices such as light-emitting diodes have been used extensively in communication equipment for a wide variety of applications requiring some form of visual indicating means. For example, light-emitting diodes have been used in place of switchboard, key button or similar lamps. (See U.S. Pat. No. 4,054,814 to C. R. Fegley et al. assigned to the assignee of record.)
Such devices have also been used for indicating that a circuit protective device, such as a fuse, has been subjected to an electrical overload condition. (See U.S. Pat. No. 4,025,888 to Judd et al., assigned to Bell Telephone Laboratories and the aforementioned U.S. Pat. No. 4,054,814.) Also, fuses have been extensively used to protect communication and other electrical devices.
It is desirable to simplify the assembly techniques of these prior art devices to thereby reduce this cost. It is also desirable to package the fuse and the light-emitting diode in the same housing to aid in the simplification of such devices.
Further, it is advantageous to assemble these devices in a lead-frame environment, wherein a portion of the lead frame is formed about the bases of the devices to form contacts for connecting them to external circuits. And in the simplification of these devices, it is advantageous to bond a light-emitting diode chip directly to a current-limiting chip, both chips being bonded to another portion of the lead frame.
In circuit protective devices have electroluminescent display elements such as light-emitting diodes, it is advantageous to have light from such diodes pass not only laterally out of the bases of the devices, but also axially out of its ends. This aids in determining which of many such devices has been subjected to an electrical circuit overload condition regardless of whether such devices are viewed laterally or axially. And this is particularly important if the devices are located in a generally dark inaccessible location, such as under or behind telephone switchboards or control cabinets or under the dashboard of a car.
Moreover, it is desirable to indicate the current carrying capacity of combined electroluminescent display and circuit protective devices. This may advantageously be done with a color-coding scheme wherein the color of the light emitted from the device corresponds with the color of a band on the device indicating the current carrying capacity of the device.